There are many causes of a reduction in kidney function and it is essential that corrective action is taken as early as possible by appropriate medical intervention so as to minimise as far as possible the deleterious consequences, which include total renal failure and a need for dialysis and ultimately kidney transplant. For example, an abrupt reduction in kidney function occurs frequently following cardiothoracic (CT) surgery. Thus, Acute Kidney Injury (AKI) is common following CT surgery occurring in 7-42% of patients (Mora Mangano, C. et al (1998) Ann Intern Med 128:194-203; and Tuttle, K. R. et al (2003) Amer J. Kid Dis 41:76-83.) Small changes in serum creatinine have been shown to correlate with increased morbidity and mortality, following CT surgery (Lassnigg, A. et al (2004) J. Am Soc Nephrol 15; 1597-1605).
Measurement of creatinine is the standard test in the clinic for measuring kidney function. If kidney function is abnormal, creatinine levels will increase in the blood due to decreased excretion of creatinine in the urine. Creatinine levels vary according to a person's age, size and muscle mass. In acute conditions build up of creatinine in the blood may take up to 24-72 hours to occur.
Patients who develop severe AKI requiring Renal Replacement Therapy (RRT), after CT surgery have a greatly increased in-hospital mortality (63%) compared to those with non-dialyzed AKI (19%), or stable renal function (0.9%) (Mora Mangano, C. et al (1998) supra).
Koyner, J. L. et al (poster presentation at American Society of Nephrology, Renal Week 2007, Oct. 31-Nov. 5, 2007, Moscone Center, San Francisco, Calif.) have investigated urinary Cystatin C (CyC) and Neutrophil Gelatinase—Associated Lipocalin (NGAL) in patients with AKI following adult cardiac surgery. Koyner, J L et al found that urinary CyC excretion increases in the early post-operative period following adult CT surgery and concluded that urinary CyC may be a useful early biomarker for the development of AKI as it appears to correlate with the severity of AKI and thus the future need of RRT. Similarly, Koyner, J L et al found that urinary NGAL in the early post-operative period appears to predict the development of AKI and correlate strongly with the future need of RRT.
U.S. Publication 2004/0219603 discloses that urinary NGAL measured within two hours of cardiac surgery was predictive of Acute Renal Failure (ARF) as reflected by serum creatinine peak, which occurs several hours or even days later.
Koyner J. L. et al (2007) (supra) show that for both CyC and NGAL the main increase occurs in the ICU (Intensive Care Unit) phase post CT surgery.
Eijkenboom, J. J. A. et al (2005) Intensive Care Med 31:664-667 show that an increase in Glutathione S-Transferase (GST), excretion following cardiac surgery was not correlated with changes in plasma creatinine and is not associated with clinically relevant renal injury.
Davis, C. L. et al (1999) J Am Soc Nephrol 10: 2396-2402 disclose that urinary GST excretion increased in most patients after CPB, however, this increase was not associated with the development of clinically apparent ARF.
There is a need for a biomarker which predicts elevated blood creatinine levels resulting from an abrupt reduction in kidney function and thus the development of AKI at the earliest stage post CT surgery, ideally at zero hours in the recovery room and prior to transfer to ICU or earlier, namely intraoperatively, so as to enable corrective action to be taken as soon as possible for those patients who develop AKI with the attendant consequences.
Currently no drug therapy is available for counteracting the effects of a reduction in kidney function as seen, for example in post CT surgery. Accordingly, the surgeon and other attending medical professionals will endeavour to reduce the effects of renal ischemia or other causative effect by managing fluid levels and other physiological parameters. However, as indicated above, frequently, if such measures do not prove successful, the patient will require RRT, namely dialysis.